The present invention relates to an electrically insulated coil, having a high shear strength and a high heat resistance and a high withstand voltage, wherein a thermosetting resin composition of a repeatedly usable one-component epoxy resin is used, and to an electric rotating machine using the coil. The invention also relates to a method for producing a totally impregnated rotating coil.
Demands for making high-voltage rotating machines, such as electric vehicles and induction motors for general industries, with a small scale, a light weight and a low cost have increasingly escalated. The methods for manufacturing the stator coil and rotor of such high-voltage rotating machines are broadly grouped as follows: (1) in a single prepreg process, after prepreg mica tapes are wound around a stack of insulated conductors, the prepreg mica tape wound around a conductor stack is heated and the resin is hardened. Then, the cured electrical insulating coil is placed into an iron core slot; in a single impregnation process a after insulating mica tapes have been wound around a stack of insulated conductors, the stack is impregnated with a thermosetting resin composition in a tank, and the resulting stack is heated and the resin is hardened. Then, the cured electrically insulated coil is placed into an iron core slot; and (3) in an total impregnation process, after the insulating mica tapes have been wound around a stack of insulated conductors, the stack is placed into an iron core slot, a wedge is inserted into the external circumferential groove of the iron core slot to connect the electrical insulating coil to the external end part of the iron core, followed by impregnating the assembly with a thermosetting resin composition in a tank, and then curing the electrical insulating coil and the iron core slot in their integrated state with a thermosetting resin composition. In the stator of the total impregnation type, the iron core and the electrically insulated coil are integrated together because the cured material of the impregnating thermosetting resin composition is filled in the space between the electrically insulated coil and the iron core slot. Therefore, the heat conductivity between the electrically insulated coil and the iron core is so high that good cooling performance can be procured and the process can be simplified, advantageously from the aspect of production of small-scale and light-weight equipment at a low cost. Thus, such a process is now being pursed as a first choice as the insulating process for small scale to medium scale high voltage electric rotating machines of high-pressure.
Thermosetting resin compositions for impregnating electrical insulating coils to be used for the single impregnation process or total impregnation process are required to satisfy the following conditions: 1. the compositions should have a low viscosity (at 10 poise or less during impregnation) so as to readily impregnate such electrically insulated coils; 2. the compositions should never generate volatile substances so as to avoid the occurrence of a void (space) at a course of heating and curing; 3. the pot life, namely the usable time, should be as long as 25 days or more; 4. the heating and curing time should be short; 5. the electrical and mechanical performance needs to be great; 6. the compatibility with the insulating tape base material should be comfortable; and 7. the cured compositions should be highly thermally resistant, in other words, the cured compositions should have short-term and long-term thermal deterioration characteristics above 155.degree. C.
A thermosetting resin composition principally comprising an acid anhydride and an epoxy resin has been used from the aspect that, as a thermosetting resin composition for impregnating electrically insulated coils of rotating machine, the composition has a low viscosity with ready workability and handleability during impregnation and exerts a variety of great performance characteristics after curing.
The manufacture of electrically insulated coils requires more than 1000 kg of impregnating thermosetting resin composition in order to immerse the whole coils.
However, the amount of consumption at one impregnation is at most about several %, so the remaining amount should be recovered, followed by fresh addition thereof in an amount corresponding to the consumption, so as to use the composition efficiently.
Although such a thermosetting resin composition of an acid anhydride-hardening epoxy resin has a longer usable time, the resin composition requires a catalyst because of its poor curing profile. Generally, however, direct addition of a curing catalyst into a thermosetting resin composition elevates the viscosity of the thermosetting resin composition during the impregnation and storage. Thus, the composition reached an unusable state in several days.
Therefore, a so-called coating process to deposit a curing catalyst onto an insulating tape base material, as described in Japanese Patent Laid-open No. Sho 62-1124452, has been selected generally.
If an electrically insulated coil is prepared by the coating process of a curing catalyst, there tends to be a smaller amount of the curing catalyst in the thermosetting resin composition impregnated into the space between an iron core slot and the electrically insulated coil, in the thermosetting resin composition at a part spaced from the insulating tape base material layer and with a lower curing catalyst level, and in the thermosetting resin composition on the surface layer of the electrical insulating coil, the curing therein is insufficient. Therefore, satisfactory performance cannot be attained. Because the variation of the curing catalyst level is large in the insulating tape base material, the variation of the performance of the insulating layer cannot be reduced.
Research into so-called latent curing catalysts, which are stable at ambient temperature but rapidly effect curing on heating, have been conducted actively; therefore, proposals have been made for use of metal imidazolate, as described in Japanese Patent Laid-open No. Sho 48-79300; tetra-onium salt, as described in Japanese Patent Laid-open No. Sho 50-110500; an addition product of imidazole and a first transition metal coordination compound, as described in Japanese Patent Laid-open No. Sho 50-11298; arsonium salt, as described in Japanese Patent Laid-open No. Sho 50-117898; chromium (III) chelate, as described in Japanese Patent Laid-open No. Sho 51-8400; metal acetylacetonate, as described in Japanese Patent Laid-open No. Sho 52-130899; organosiloxane compounds and aluminium acetylacetonate, as described in Japanese Patent Laid-open Nos. Sho 53-125500 and 56-4625; a reaction product resulting from the reaction of a metal acetylacetonate and an acid anhydride with polyethylene glycol monoalkyl ether; a reaction product resulting from the reaction of a metal acetylacetonate and an acid anhydride with polyethylene glycol monoalkyl ether , as described in Japanese Patent Laid-open No. Sho 60-108418; a reaction product resulting from the reaction of a metal acetylacetonate and an acid anhydride with an aliphatic alcohol, as described in Japanese Patent Laid-open No. Sho 61-4722; occult hydrazine curing catalysts as described in Japanese Patent Laid-open No. Sho 62-270616; an latent curing catalyst produced by the reaction of an epoxy resin compound with dialkylamine to prepare an addition compound, which is then pulverized in powder, as described in Japanese Patent Laid-open No. Sho 64-40516; and the use of a borotrifluoride complex compound and a microcapsule-type latent curing agent in combination, as described in Japanese Patent Laid-open No. Hei 3-281625.
However, these catalysts have not necessarily been satisfactory in a practical sense, because not any of these catalysts can have both a desired stability and curing performance together.